This invention relates to the provision of asphaltic concrete in a state or condition suitable for paving application or the like, and particularly to the production of asphaltic concrete in condition for application from initially solid asphaltic material. In a specific sense, the invention is directed to an asphalt reclamation unit for this purpose, and more particularly to such a unit having a discharge feed and improved hot air flow.
It is known to heat chunks or other pieces of initially solid, cold asphaltic material (i.e. asphaltic material initially at ambient atmospheric temperature) to provide asphaltic concrete for paving or like application, e.g. for patching. For example, useful asphaltic concrete can be reclaimed in this way from chunks of used asphaltic concrete paving. Desirably, the produced material should be a substantially homogeneous, soft or flowable mass capable of being spread easily and evenly to constitute a patch.
Prior procedures for reclaiming used asphaltic material have involved rapid heating. Difficulties associated with such prior practice have included excessive heating of the material, oxidation of the liquid component thereof, segregation of components, and/or burning. These disadvantages have led to nonhomogeneous or otherwise defective products.
U.S. Pat. Nos. 3,386,435 and 3,577,976, both assigned to the present assignee, describe units for storing materials such as asphaltic concrete at an elevated temperature. In these units, the asphaltic material is contained within an inner enclosure which is surrounded by an outer enclosure that defines spaces or passages beneath and on all sides of the inner enclosure. Air, heated by an infrared energy source beneath the inner enclosure, flows through these spaces and/or passages to minimize the thermal gradient across the wall of the inner enclosure and thereby to retard heat loss from the contained hot asphalt. The rising heated air is introduced to the top of the inner enclosure through plural horizontally spaced apertures arranged to provide a flow of heated air across the top of the contained asphalt, for further minimizing the heat loss. As will be understood from the cited patents, the purpose of these structures is primarily to maintain the elevated temperature of a charge of asphaltic material supplied to the inner enclosure in initially heated condition, and not to heat an initially cold charge to a suitable temperature for application.
U.S. Pat. No. 2,496,113 describes a heater melting bituminous material wherein heated gas is passed through an essentially horizontal flue system extending within or beneath the charge of material to be heated and is then conducted upwardly at one end of the heater so as to be directed across the surface of the charge.
U.S. Pat. No. 4,418,682 and related U.S. Pat. No. 4,445,848, both assigned to the present assignee, disclose an asphaltic reclamation unit having inner and outer enclosures spaced from each other to form passageways therebetween to provide a gas space for heated air to flow from a heating source. Unheated asphaltic material is loaded into the open top of the unit and is heated and removed by way of doors at the back wall of the unit. The front wall in such units slopes upwardly so that the material collects at the back. This arrangement limits the capacity of the reclaimer, and the material is removed manually.